A. Technical Field of the Invention
The present invention relates to a propulsion system for a magnetically levitated or suspended vehicle. More particularly, a linear DC motor-type propulsion system uses current variation for speed control. The propulsion system can in part be supported by electromagnetic or electrodynamic suspension systems, and current transients or dynamic braking can be used to provide power to auxiliary electrical devices on the vehicle.
B. Description of the Related Art
Presently, magnetic suspension or magnetic levitation ("maglev") systems use linear AC synchronous-type machines for propulsion. These systems generally incorporate three phase coils with cores laid along a guideway and powered to create a moving magnetic field. The moving magnetic field "pulls" magnets on a vehicle to induce vehicle movement, and speed control is obtained by varying the frequency and phase of the current powering the coils.
Consider the following examples. U.S. Pat. No. 3,768,417, "Transportation System Employing an Electromagnetically Suspended, Guided and Propelled Vehicle" (THORNTON & KOLM); U.S. Pat. No. 3,771,033, "Apparatus for Propelling A Movable Body in a Suspended State At A Very High Speed" (MATSUI); U.S. Pat. No. 3,850,109, "Transportation System Employing Magnetic Levitation, Guidance And Propulsion" (THORNTON); U.S. Pat. No. 3,871,301, "Stabilization and Ride Control of Suspended Vehicles Propelled by a Linear Motor" (KOLM); U.S. Pat. No. 3,913,493, "System for Propelling Train by Linear Synchronous Motor" (MAKI); and U.S. Pat. No. 3,914,669, "System for Attenuating Vertical Oscillations of a Suspended Track Bound Propulsion Vehicle" (HOLT) all use linear synchronous type machines as propulsion systems.
To focus for a moment on one of these patents, MATSUI uses a vertical ladder type of structure with overlapped, diamond-shaped synchronous coils. Different coil segments are pulsed with DC at separate times to create a moving magnetic field equivalent to that produced by standard synchronous coils. Thyristors are used to preclude the excitation of the coils with variable frequency. Pushing more current through the MATSUI coils without speeding up the excitation of the thyristors will not make the MATSUI vehicle go faster.
As articulated in the above-referenced patents, AC synchronous machine propulsion systems are known to have certain limitations and drawbacks. Such systems, for example, are sensitive to air gap fluctuations between the vehicle and the rail(s). These fluctuations pose design problems for electrodynamic suspension systems in which vehicle lift height varies with speed.
Prior to the invention disclosed herein, no teaching is known to disclose a vehicle propulsion system in which current in a current rail assembly interacts with a fixed magnetic field of the vehicle to propel the vehicle, and wherein the current in the current rail assembly, the magnetic field strength, or both can be increased to make the vehicle go faster.